reflections on learning to help others learn

Holography

There is a long tradition at my school of students creating holograms as a final activity in physics. Everyone gets to make their own and keep it. I have heard several alumni mention that they still have their hologram. Just this week, an alumni who is also a dean remarked that he still has his hologram from 20 years ago. Sometimes the purpose of an activity is learning; sometimes, just to inspire. This is the later.

I’m not sure how we first made holograms, but at some point in the distant past, now retired teachers must have attended a holography workshop led by Dr. Jeong from Lake Forest College. A couple of summers ago, I attended a Chicago Section AAPT meeting and was surprised to learn that Dr. Jeong was leading the workshop!

For years we have been making reflection holograms. These usually turn out well. The disadvantage is that there isn’t much depth and, therefore, the 3-D effect isn’t as dramatic. The advantage is that reflection holograms are easily visible in white light (sun light is especially effective).

Last year, after attending Dr. Jeong’s workshop, we decided to try and also make transmission holograms. Dr. Jeong actually demonstrated how to make an “omnigram” which is a combination of a reflection hologram and a transmission hologram on a single slide. We tried this, but only the transmission holograms were visible. The transmission holograms were amazing. They have an incredible depth which allows larger objects (or a collection of small objects) to be captured. The disadvantage is that a laser is required to view the hologram (a green laser pointer works better than a red one).

This year, we provided students an option to make either type of hologram. They split about 50-50. As the price of laser pointers continue to fall, we may soon only make transmission holograms.

We order all of our supplies from Integraf. We use the PFG-03M holography slides, the JD-4 processing kit, and the DL-4B laser diode. The setup for transmission holograms is relatively simple. I have detailed photos of the slide holder (on the left) and laser (on the right). The objects are positioned between the slide holder and laser. In the back, is the shutter which blocks the laser light and consists of foam board covered with black felt with a base of two large binder clips.

I built the slide holder from a 2.5″ picture frame. The picture frame is painted a flat black. Black backing material is glued to the top of the picture frame to ensure that laser light does not enter the sides of the slide. The picture frame is secured to a base which is a tea tin filled with sand and covered with black felt. The picture frame backing is slid behind the slide in the frame to secure the slide (emulsion side faces the scene).

The diode laser is secured by a clothespin in a tea cup filled with sand. It is is positioned on a base which consists of three physics texts covered with black fabric. I added a switch and a two-pin connector to the battery box which results in a more reliable connection and easier operation.

If you are interested in making your own holograms, feel free to contact me and I’ll try to answer any questions that you may have. Dr. Jeong is very approachable and provided several tips based on questions that I posed.

Update

I realized that it would be helpful to show some examples of these holograms. It was challenging to photograph them, but here is my best attempt for a transmission hologram: